1. Field of the Invention
The present invention relates to a toner supply roll for use in an electrophotographic apparatus such as a copying machine, a printer or a facsimile machine.
2. Description of the Art
In an image forming apparatus such as a copying machine, a printer or a facsimile machine, an image forming operation is performed, as shown in FIG. 3, by forming an electrostatic latent image of an original image on a surface of a photoreceptor drum 12, causing a toner to adhere on the electrostatic latent image to form a toner image, transferring the toner image onto a sheet, and fixing the toner image on the sheet. For the formation of the toner image, a predetermined toner (developer) is supplied onto a surface of a developer roll 17 from a toner box (not shown) by a toner supply roll 11, and then transferred onto the surface of the photoreceptor drum 12 from the surface of the developer roll 17. The thickness of a layer of the toner formed on the developer roll 17 is controlled by a layer formation blade 18. A portion of tile toner remaining on the surface of the developer roll 17 is scraped by the toner supply roll 11 thereby to be fed back into the toner box. Thus, the toner supply roll 11 is essential for a full color image forming apparatus. Conventionally, the toner supply roll 11 includes a shaft and a urethane foam layer provided on an outer peripheral surface of the shaft.
For evaluation of the toner supply roll 11, it is a conventional practice to measure the outer dimensions of the toner supply roll 11 by means of a laser beam. Further, the hardness of the urethane foam layer is also measured for the evaluation of the properties of the toner supply roll (see, for example, Japanese Unexamined Patent Publication No. 9-274373 (1997)).
However, a toner supply roll judged to have little numerical variation in dimensions and in hardness by the aforesaid evaluation methods is often determined to be inferior and unacceptable when actually used for image formation. That is, it is impossible to accurately predict whether a toner supply roll which satisfies dimensional and hardness requirements as judged by the conventional evaluation methods, is liable to cause the imaging failure when used for image formation. Hence, it is desirable to define an additional property requirement for a toner supply roll for assuredly preventing imaging failure.
In view of the foregoing, it is an object of the present invention to provide a toner supply roll which is free from the occurrence of imaging failure and a method for determining the same.